This invention pertains to heat exchangers and other forms of energy recovery apparatus, such as a chiller, wherein a low-cost unit formed of relatively simple components maximizes the saving of energy in both the manufacture thereof as well as in use thereof.
Many different devices are known for obtaining heat exchange between a pair of fluids including units in which one fluid is caused to flow along the wall of a shell and another fluid is brought into heat exchange relation with the shell. One example of such structure is shown in Burdick U.S. Pat. No. 1,694,370 wherein a series of vertical tubes have one fluid flowing along the interior of the tube wall and another fluid flowing vertically downward along the outer surface of the wall. This device has many structural and operational disadvantages. It is expensive to construct with the requirement for a main enclosure for the system and has many sealing surfaces to maintain the separation of fluid spaces. Additionally, the parallel flow of the fluids does not provide as high efficiency of heat exchange as can be obtained by means of a cross-flow or counter-flow of fluids.
The Dawson U.S. Pat. No. 3,502,140 shows a heat exchanger for two liquids having a relatively complex structure for obtaining a falling film of liquid and additionally requiring a primary enclosure for the structure.
A primary feature of the invention disclosed herein is to provide a heat exchanger having a simple circuit in which fluids are maintained separate and in confined paths with savings in energy in manufacture of the heat exchanger as well as utilization thereof and with low-cost construction and operation and with the capability of handling a plurality of separate fluids.
More particularly, the heat exchanger has a basic shell to receive fluid and surrounding fluid passages which may be of simple construction and in heat exchange relation with the shell. The unit may be insulated simply by applying insulation to the exterior of the surrounding fluid passages thereby essentially eliminating heat losses when adequate insulating material is applied. The cost to insulate is minimal because of the simple, regular, small surface area to be insulated and the heat exchange efficiency is maximized.
More particularly, the shell can be a tubular member, such as standard pipe or tubing of a size required for the particular operation, and the fluid in heat exchange relation with the pipe can be conducted through preformed fluid channels which are closely fitted about the pipe and with optionally usable heat transfer promotion medium therebetween, such as a silicone or grease with aluminum oxides which are commercially available. A simply constructed partition member is inserted within the pipe to provide upper and lower compartments and a fluid connection delivers fluid to the upper compartment. Passage means provided along the edges of the partition member permit flow of fluid from the upper compartment into the lower compartment by flowing along the interior of the shell wall. The partition member may be formed of a longitudinal section of a pipe of greater diameter and formed with notches along its opposite edges and then fitted into the shell to provide the upper and lower compartments.
With the structure disclosed herein, the heat exchange can be for either heating or cooling of a medium, either within the shell or within the fluid containment means disposed therearound.
The heat exchanger has high heat exchange efficiency because of combined counterflowing and cross-flowing action of the respective fluids. With the flow of fluid down the shell wall along the entire length thereof, the temperature within the shell is capable of being maintained uniform which results in minimum time for cooling of fluid in the surrounding fluid containment means for equivalent heat exchange boundary area in other types of heat exchanger, all other factors being equal.
A primary application of the heat exchanger is in use thereof as a chiller as usable in an absorption refrigeration and air conditioning system, as shown in my prior U.S. Pat. No. 3,661,200, dated May 9, 1972. In the water chiller disclosed therein, liquid ammonia and helium gas are delivered to the chiller and are caused to chill a liquid, such as ethylene glycol/water, a typical antifreeze solution, for use in the air conditioning system.
In the chiller, the liquid ammonia evaporates and combines with a warmer helium gas delivered to one end of the chiller and the combined cold vapors of ammonia mixed with the helium pass from an opposite end of the chiller. Use of the construction disclosed herein results in a highly efficient energy saving unit with low pressure losses throughout the unit. The higher refrigerant pressures that exist in the system are contained within the shell and, therefore, the conduit means containing the liquid (ethylene-glycol solution) to be cooled need not have substantial structural strength. With the horizontal disposition of the structure, the unit can handle three fluids, with two fluids within the shell actually passing in opposite directions therein.
The disclosed heat exchanger has utility in many different systems. As an example, several of the heat exchange units can be arranged in one or more horizontally-spaced rows and in horizontal positions and with units positioned one directly above another in a row. The vertical space between units in a row would be approximately one-half the diameter of a shell. Liquid refrigerant is introduced into the upper compartment of each horizontal unit. The refrigerant flows horizontally the length of the shell upper compartment and flows down the interior of the shell wall in the lower compartment, as earlier described for the chiller application. The refrigerant is evaporated from the entire length of the lower compartment by exchange of heat through the shell wall from a warmer fluid flowing normal to the longitudinal axes of the horizontally-disposed heat exchanger units. This flow is through a formed contained fluid path, such as a duct, the boundaries of which are the ends of the horizontal lengths of the heat exchanger units and the vertical distance from the bottom of the lowermost heat exchange unit to the top of the uppermost unit. Because of the higher efficiency of the heat exchange units disclosed herein, it is possible to use a minimal number of rows of units for a typical air conditioning application in which the refrigerant is evaporated within the lower compartments of the shells by exchange of heat from the warmer fluid (air) flowing normal to the longitudinal axes of the heat exchange units.